Great work. I'll echo what Herb said, these multisection caps have an inverse reaction to their stationary ESR rating. Essentially, if it sits for a year or two without use, the ESR value will show rather high. However, once power is applied the caps will reform after a few days of regular use the capacitance value will settle and the ESR value will go down considerably. What that means is they'll warm up due to the resistance, but as they reform you'll notice that they go cold - this is when they've been reformed. In the same way, anytime you have an amp running and the multisection cap is hot, it has developed permanent series resistance, time to replace.
Phil, by and large , the F&T caps get better with use. I check leakage and ESR with my Sencore LC71 prior to install. After some time , they measure better with some hours of use. I have several newish CE caps in my junk box that got leaky in a high voltage use situation. BTW Vishay offers a HVR series metal film resistor specifically for high voltage circuits. In a three wire power cord , consider using a bridge rectifier as a ground lifter ( 1.2 volts ) rather than a direct ground connection to the chassis. This eliminates most ground loops but keeps the user safe.
I assume that you will get into this in the testing, but I would be curious to see if the inrush limiter limits current during max transients, maybe you can chart across the limiter. Might be interesting to see a 50hz square wave into a 4ohm(?) load at full power. I probably would have chosen a thicker silicone flexible cord purely for aesthetics, but that would be a minor nit-pic. You do very nice work. I am envious of your test gear collection!
Thanks, I did spend quite a bit of time yesterday thinking about/experimenting with that, when I started comparing the rebuilt amp to the stock one. One thing I wasn't aware of, as I don't have much experience with McIntosh gear, a friend reminded me that McIntosh has been using ICL's in their amps for years, employed in the same fashion (on the primary side) to no detriment. The MK3 measured 1.15a idle and 1.75a full loaded, which puts the CL-80 between 0.4 and 0.6% load, so per the CL-80 data sheet that should be around 1.8 - 1 ohm resistance. The other thing is, these mk3s still have the 30/20/20/20 filter caps, so I think that’s more of an issue during transients than the cl-80. Next video will probably be more traditional tests (thd+n at various frequencies, frequency response etc). I'll try to do a follow up on the CL-80 in the future once I have time to get all my facts straight. I can do some experiments with my Scott 299 or Dynaco ST-70 if I give these MK3's back before that.
It's such a shame to think the owner put his trust in the previous "expert" only to have him do such shabby work. It's a good thing these timeless units are in good hands now.
Do I see some Shinkoh resistors ? I hated working on tube amplifiers that were hacked before i got them to repair .... Often they asked for retubeing but when opend up I saw the real horror and messing up done by so called tech repair shops .......... Thank you for the upload. Upgrading ( expensive components ) must be done with experience and real evalution after the work..........sometimes so called better may be your worst enemy.....or exposing the limits and intrinsic distortion of a circuit....my attitude todaéy is only to try an upgrade aon an amploifier when the mp performs well and sound, when I DO NOT feel the need to upgrade ...that is mostly when it realy works.
Thanks for the feedback, glad you enjoyed the video. Nah, no exotic parts like Shinkoh resistors. With the exception of a couple Dale RLR20 resistors I had in stock, all parts I used in the rebuild are current production parts available from DigiKey, just chosen as best bang for the buck. The larger 1W blue resistors are Yaego MFR100, and the smaller 0.6w's are Vishay MBB0207 series. There is a single Holsworthy (the black 270k) as that value wasn't in stock from the MFR100 line, and the 1.5M resistor is a Vishay HVR37. I'm not so much into 'upgrading' for the sake of audio quality as I am just trying to make the units rock solid reliable and meet or slightly beat the factory specs. Which in most units I've worked on over the past few years that had carbon comps in them, means replacing all of the resistors due to drift...even the good ones like Allen Bradley's I see drift out of spec these days...
Great work. I'll echo what Herb said, these multisection caps have an inverse reaction to their stationary ESR rating. Essentially, if it sits for a year or two without use, the ESR value will show rather high. However, once power is applied the caps will reform after a few days of regular use the capacitance value will settle and the ESR value will go down considerably. What that means is they'll warm up due to the resistance, but as they reform you'll notice that they go cold - this is when they've been reformed. In the same way, anytime you have an amp running and the multisection cap is hot, it has developed permanent series resistance, time to replace.
Phil, by and large , the F&T caps get better with use. I check leakage and ESR with my Sencore LC71 prior to install. After some time , they measure better with some hours of use. I have several newish CE caps in my junk box that got leaky in a high voltage use situation. BTW Vishay offers a HVR series metal film resistor specifically for high voltage circuits. In a three wire power cord , consider using a bridge rectifier as a ground lifter ( 1.2 volts ) rather than a direct ground connection to the chassis. This eliminates most ground loops but keeps the user safe.
Great video Phil! So cool to see the inrush current testing before and after. Keep up the great work.
Thanks Ben! Your recent videos on the VTA ST-70 have been a great inspiration on some other tests I plan to perform on these guys.
I assume that you will get into this in the testing, but I would be curious to see if the inrush limiter limits current during max transients, maybe you can chart across the limiter. Might be interesting to see a 50hz square wave into a 4ohm(?) load at full power. I probably would have chosen a thicker silicone flexible cord purely for aesthetics, but that would be a minor nit-pic. You do very nice work. I am envious of your test gear collection!
Thanks, I did spend quite a bit of time yesterday thinking about/experimenting with that, when I started comparing the rebuilt amp to the stock one. One thing I wasn't aware of, as I don't have much experience with McIntosh gear, a friend reminded me that McIntosh has been using ICL's in their amps for years, employed in the same fashion (on the primary side) to no detriment. The MK3 measured 1.15a idle and 1.75a full loaded, which puts the CL-80 between 0.4 and 0.6% load, so per the CL-80 data sheet that should be around 1.8 - 1 ohm resistance. The other thing is, these mk3s still have the 30/20/20/20 filter caps, so I think that’s more of an issue during transients than the cl-80. Next video will probably be more traditional tests (thd+n at various frequencies, frequency response etc). I'll try to do a follow up on the CL-80 in the future once I have time to get all my facts straight. I can do some experiments with my Scott 299 or Dynaco ST-70 if I give these MK3's back before that.
It's such a shame to think the owner put his trust in the previous "expert" only to have him do such shabby work. It's a good thing these timeless units are in good hands now.
Do I see some Shinkoh resistors ?
I hated working on tube amplifiers that were hacked before i got them to repair ....
Often they asked for retubeing but when opend up I saw the real horror and messing up done by so called tech repair shops ..........
Thank you for the upload.
Upgrading ( expensive components ) must be done with experience and real evalution after the work..........sometimes so called better may be your worst enemy.....or exposing the limits and intrinsic distortion of a circuit....my attitude todaéy is only to try an upgrade aon an amploifier when the mp performs well and sound, when I DO NOT feel the need to upgrade ...that is mostly when it realy works.
Thanks for the feedback, glad you enjoyed the video.
Nah, no exotic parts like Shinkoh resistors. With the exception of a couple Dale RLR20 resistors I had in stock, all parts I used in the rebuild are current production parts available from DigiKey, just chosen as best bang for the buck. The larger 1W blue resistors are Yaego MFR100, and the smaller 0.6w's are Vishay MBB0207 series. There is a single Holsworthy (the black 270k) as that value wasn't in stock from the MFR100 line, and the 1.5M resistor is a Vishay HVR37.
I'm not so much into 'upgrading' for the sake of audio quality as I am just trying to make the units rock solid reliable and meet or slightly beat the factory specs. Which in most units I've worked on over the past few years that had carbon comps in them, means replacing all of the resistors due to drift...even the good ones like Allen Bradley's I see drift out of spec these days...